It is known in the art to render polycarbonate resins flame retardant and non-dripping by admixing therewith an organic alkali metal salt or an organic alkaline earth metal salt of sulfonic acid, and a fluorinated polyolefin (Application Ser. No. 949,964 filed Oct. 10, 1978, now abandoned and assigned to the same assignee as the instant application). However, polyester-carbonate resins are quite different from polycarbonate resins. Thus, for example, polyester-carbonates have a higher heat distortion temperature under load (generally from about 50.degree. F. to about 60.degree. F. higher) than polycarbonates, and are usually more difficult to process (because of their higher intrinsic viscosity) than polycarbonates.
It is this difference in properties, especially the heat distortion temperature, that provides one of the main reasons for using polyester-carbonates in place of polycarbonates in certain applications. This is particularly true where there is a high temperature environment. In spite of the disadvantage of the more difficult processability of the polyester-carbonate resin it is still preferred over the polycarbonate resin in these applications because of its higher heat distortion temperature. However, this main advantage of polyester-carbonates makes it especially important that they be made flame retardant and non-dripping since they are used in high temperature environments where the chances of ignition and burning are increased.
It is well known to those in the field that the area of modification of the physical properties of a polymer, e.g. flame retardance, by the addition thereto of certain additives is largely an empirical art rather than a predictable science with little, if any, predictability on the effects a certain additive will have in a particular polymer system. Thus, while a particular additive may have one effect in one polymer system the same additive may well produce entirely different results when used in another and different polymer system. Likewise, two rather closely related additives may produce entirely different results when admixed with the same polymer.
The present situation is even more complicated in that two entirely dissimilar additives, i.e. (i) an organic alkali metal salt of sulfonic acid or an organic alkaline earth metal salt of sulfonic acid, and (ii) fluorinated polyolefin, are employed.
There thus exists a need for flame retardant and non-dripping aromatic polyester-carbonate resins.